The capacity of stem cells to self renew and differentiate into additional cell types has made them a subject of great interest to life scientists. Germline stem cells are a category of stem cells that give rise only to cells associated with the germline, including egg and sperm, and thus are also important for developmental reasons. Germline stem cells have historically proven challenging to study because of their scarcity in organisms. Copidosoma floridanum, a parasitic, polyembryonic wasp, is a promising organism in which to study germline stern cell regulation because a) they produce germline stem cells and their progenitors in relative abundance and b) they have two striking developmental processes associated with changes in germline regulation. First C. floridanum is polyembryonic meaning that thousands of offspring develop clonally from a single egg and therefore so too do thousands of germline stem cells. Polyembryony is achieved, in part, by increased proliferation early in embryogenesis. Secondly, offspring of the same brood develop into morphologically distinct larval castes. Recent evidence indicates that germ plasm, the cytoplasm defining germline stem cell precursors, is required for both of these processes. Ablation of germ plasm containing cells in C. floridanum decreases proliferation and eliminates differentiation of the reproductive caste. Here, I hypothesize that changes in early stem cell regulation are responsible for polyembryony and caste differentiation in this species. The specific aims of this proposal are to evaluate my hypothesis by testing explicit predictions about how germ plasm containing cells should act during development using a combination of observational and functional studies. The long-term goals of my study are to understand the function of germline and other stem cells during development. While germline stem cells are essential for development and have been linked to disease, very little is understood about how they are formed. This work will contribute to understanding the molecular controls of stem cells and how they vary among organisms.